Meeting Abstract
The Cane Toad, Rhinella marina, is native to South and Central America, but was introduced to Palm Beach County, Florida, for pest control circa 1935. Its range has been limited to the southern third of Florida for decades. Recently, we have documented established populations of this species at greater latitudes than the isothermal minimum predicted by Urban, Phillips, Kelly, and Shine (2007). As part of a study to determine what physiological adaptations have occurred to allow this northern range expansion, we examined baseline and constraint-challenged glucocorticoid levels and plasma bactericidal capability as indicators of physiological condition for populations along the invasion front. We hypothesized that R. marina populations at higher latitudes and exposed to a more temperate thermal regime would experience chronic thermal stress, yielding significantly elevated baseline glucocorticoid levels, and depressed stress and immune response. Plasma samples were collected from R. marina specimens from Miami, Lake Placid, Sebring, New Port Richey, and, Deland, Florida, representing populations along a South to North gradient. Preliminary findings indicate that both baseline corticosterone and bacterial killing ability were significantly elevated in more northern populations, indicating that although toads in more northern populations have elevated glucocorticoid levels, this does not seem to depress an aspect of their innate immune response.
